1. Field of the Invention
The present invention relates to a combinational weighing device combining groups of objects having different weights with each other to reach a desired weight. More specifically, it relates to a technique of controlling the quantity of each group of objects in a combinational weighing device.
2. Description of the Background Art
A combinational weighing device is employed in order to bag objects such as sweets or vegetables having different weights by a desired total weight (target measured value). The combinational weighing device temporarily disperses objects to a plurality of groups, weighs each group of objects and selects a combination of values of each group for implementing the target measured value.
Briefly stated, a cross feeder of a general combinational weighing device supplies objects introduced into the device to a dispersion feeder. The combinational weighing device dispersively discharges the objects supplied to the dispersion feeder to a plurality of radiation feeders and thereafter transports the same to each measuring hopper through a pool hopper. Each measuring hopper measures the weight (hereinafter referred to as “transport quantity”) of the groups of objects transported from the corresponding radiation feeder and outputs the result of the measurement to a control part consisting of a CPU or the like. The control part selects the optimum combination of measuring hoppers on the basis of the result of the measurement and instructs the selected measuring hoppers to introduce the group of objects. The measuring hoppers instructed by the control part open on-off gates for introducing the group of objects into a collecting chute. The combinational weighing device bags a plurality of groups of objects introduced into the collecting chute through a discharge chute. In such a combinational weighing device, the probability of presence of combinations of the measuring hoppers attaining a target measured value depends on the transport quantity of each group of objects introduced into the respective measuring hoppers. In this combinational weighing device, therefore, it is important to properly control the transport quantity in order to perform efficient combinational measurement processing.
As exemplary means for controlling the transport quantity in such a combinational weighing device, there is proposed a device for controlling the supply ability of a dispersion feeder according to a prescribed operation technique on the basis of a result of measurement received from a measuring hopper (a result of measurement of the transport quantity) thereby properly controlling the aforementioned transport quantity.
There is also proposed a device setting a target introduction number (n/2, where n represents the number of measuring hoppers provided in the device) of the measuring hoppers for attaining a proper transport quantity, comparing the number of measuring hoppers performing introduction in practice and the target introduction number with each other, regarding that the transport quantity is reduced if the number of the measuring hoppers performing introduction is greater than the target introduction number and increasing driving strength (exciting force) for a dispersion feeder.
The general combinational weighing device consumes objects substantially identical in quantity to the target measured value in one cycle by bagging due to the aforementioned processing. If the quantity (hereinafter referred to as “delivery”) of the objects discharged from the dispersion feeder to the radiation feeders during this cycle is equal to the target measured value, therefore, no oversupply/undersupply takes place in the radiation feeders or the like but the combinational weighing device most efficiently stably operates.
As a device structured on the basis of this principle, there is proposed a device driving a dispersion feeder by one cycle on the basis of a manipulated variable and obtaining the delivery currently discharged from the dispersion feeder for obtaining the manipulated variable of the dispersion feeder in a subsequent cycle so that the value reaches a target measured value.
Also when the device properly obtains and controls the manipulated variable of the dispersion feeder in the aforementioned manner, however, the delivery discharged from the dispersion feeder varies with the distributed state etc. of the objects present on the dispersion feeder. Therefore, the delivery does not reach the target measured value in practice unless the device properly controls the quantity of the objects supplied to the dispersion feeder.
In order to solve this problem, there is generally proposed a device implementing thickness (distributed state) control of objects on a dispersion feeder. For example, there is proposed a device supplying objects from a cross feeder on-off controlled on the basis of a prescribed value to a dispersion feeder through a scattering prevention cylinder. This device obtains the rate of change of a dispersed weight from the quantity (hereinafter referred to as “dispersed weight”) of the objects present on the dispersion feeder and controls the position of the scattering prevention cylinder on the basis of a result of comparison of the rate of weight change and a prescribed value thereby controlling the thickness (dispersed state) of the objects present on the dispersion feeder.
However, this device controlling the thickness of the objects on the dispersion feeder by vertically moving the scattering prevention cylinder must be provided with a driving mechanism or a position sensor capable of precisely controlling the scattering prevention cylinder, disadvantageously leading to complicatedness of the device structure.
Further, the aforementioned conventional device performs control not on the basis of the transport quantity to be controlled but on the basis of a previously set value. Therefore, control accuracy is disadvantageously reduced due to influence by working environment for the device or the like to reduce measurement efficiency.
Further, the device must be separately provided with a mechanism or the like correctly driving the scattering prevention cylinder, disadvantageously leading to complicatedness of the device structure.